Chemical Control of Pear Psylla in Pear, 2018B

The objective of this study was to assess efficacy of certified organic insecticides compared with a conventional insecticide program for control of PP in pear. This study was conducted within a 2-acre mixed-planting block of ‘Bartlett’ and ‘d’Anjou’ planted in 2007 at the Washington State University Sunrise orchard near Rock Island, WA. The block was maintained to commercial standards by weed, disease, and nutrient sprays, pruning, and under-tree sprinkler irrigation. The first spray for this study occurred at petal fall on 2 May 2018. There were five treatment types (including an untreated check) with 2 ‘Bartlett’ and 2 ‘d’Anjou’ replications each (four total replications) organized in an RCB design. All sprays were applied using an airblast sprayer (Pak-Blast, OVS McMinnville, OR) at 100 gpa. Plots consisted of four consecutive trees in the same row. Insect sampling was conducted on the two center trees of plots. PP eggs and nymphs were counted weekly from 29 May to 13 Jun by collecting 40 leaves per plot and brushing them in the lab with a leaf-brushing machine onto a revolving glass pate with undiluted dishwashing liquid. Each composite sample from 40 leaves was counted under a stereoscope. Adult PP were sampled with a beating tray in the field using four taps per replicate, each ‘tap’ referring to three strikes with a hard rubber hose on a branch, dislodging insects onto a 45 × 45 cm tray. The average number of PP adults counted on trays per replicate (four taps) was used for analysis. Data were analyzed in SAS 9.4. Response variables were PP eggs, early instars (first–third), and late instars (fourth and fifth) per leaf from leaf brushing, and adults per tap from beat trays. Mean response variables were compared within each sample date and for season-long averages (calculated for each replication by averaging across dates, omitting pretreatment counts) using generalized linear mixed models (PROC = GLIMMIX) assuming lognormal distributions (DIST = LOGN). When there were significant treatment effects (P < 0.05), means separation was performed using Tukey’s HSD multiple comparisons tests (ADJUST = TUKEY).

In comparison to the check, all spray treatments except Ecotec Plus significantly suppressed at least one PP life stage across the season (Table 1). At the 40 lb/acre rate, Celite 610 and the conventional treatment performed similarly, with lower seasonal means compared with the check for all PP life stages except late instars, whose seasonal mean counts were similar across all treatments (including the check). At the 20 lb/acre rate, Celite 610 had greater seasonal mean counts of PP early instars and adults compared with the conventional treatment, and similar seasonal mean counts compared with the check. Within individual sampling dates, PP counts did not usually show treatment differences. Before the first treatment applications, all PP life stages were present. Subsequently, all life stages tended to decrease or maintain their abundance except the adult stage, which increased in abundance across all treatments (including the check) with a peak on 24 May.

This research was supported in part by the Washington Tree Fruit Research Commission and by industry gifts of pesticides and research funding.